System and device for evened frequency emission impact distribution using a preamble-based DSS communication link

Abstract

Disclosed herein are hub-based wireless networks employing end-devices at intermediate wireless at ranges of thousands of meters, utilizing packets that include a preamble and a data payload. End-devices may be such things as keypads, door latches, occupancy monitors, sprinkler controllers and other devices controlled or monitored in a campus or a collection of buildings. A digital spread-spectrum frequency hopping rotation is used, wherein packet transmissions rotate through frequency sequences to spread radio-frequency emissions impact over a set of frequencies. A spectrum-impact-smoothed channel set is fashioned using sequences that each specify a unique preamble frequency relative to the other sequences and channels. The set is traversed as packets are transmitted, thereby distributing the focused radio-frequency emission impact of packets having long preambles over time. Detailed information on various example embodiments of the inventions are provided in the Detailed Description below, and the inventions are defined by the appended claims.

Description

BACKGROUND

In recent history, relatively inexpensive electronic devices have become available to ordinary property-owners that wish to monitor and control various aspects of their properties. A recent concept called the “Internet of Things” imagines home-related electronic devices that can be reached through the Internet, by which an environment can be controlled, e.g. lighting, temperature, digital video recorders, and many other “smart” devices. That kind of device ordinarily requires a connection to a network switch or hub, which connection can be wired or wireless.

Wireless connections to such smart devices are often desired, particularly in existing constructions, avoiding the laying of wires in existing walls and other structures. Technologies serving this purpose include low-wattage devices that communicate using the 2.4 GHz 802.11b/g “WiFi” protocol, and other more-recent and similar protocols such as Zigbee and Z-Wave. These protocols generally permit data rates of 100 k bytes per second or more, allowing for devices that transmit and forward audio and video data in substantial real-time. However with high data rates come a vulnerability to interference from other devices operating on the same radio bands, and accordingly devices using these short-range protocols are generally limited to service within a single residence or building within a distance of less than 100 meters.

Recent technologies have been developed that permit operation to an intermediate range, communicating between points that are several miles or more away, for example using the LoRaWAN protocol. In this type of network, interference reduction is achieved by using frequencies in the UHF band and by including redundancies in communication, using for example multiple sampling, multiple frequency (spread-spectrum) techniques, and/or error-tolerant protocols. The use of the UHF band avoids interference from over-the-horizon sources, while at the same time avoiding some attenuation-of-signal from water-vapor, precipitation, buildings and other physical obstructions. These redundancies and protocols necessarily reduce the data throughput such that audio and video data cannot be streamed in good quality or in real-time.

An exemplary use of intermediate-range communication is in the recent deployment of wireless utility meters. Having a utility meter that can be read without a person traveling to and visually looking at it is a substantial cost savings for a utility. For such a use a meter communicates two items of information, which are an identifier for the meter and the meter reading itself; the utility takes a pair of such items and generates a bill for a utility subscriber. Because utility bills are ordinarily generated once per month, the amount of data from a single meter is usually on the order of a few tens of bytes in that period. Thus tens or even hundreds of thousands of meters can share a single intermediate-range channel, largely without interference from other devices.

The unsuitability of existing systems at intermediate ranges for large numbers of devices, for example in the Internet-Of-Things, is an unsolved problem. Turning now to FIG. 2, two proximal short-range networks are conceptually shown, such as those constructed from devices communicating through the 802.11g protocol, for example using the Zigbee specification. In the example two property owners each operate a hub “H” servicing multiple devices “D”, and as shown in the figure the circumference of effective communication 10 of each hub is proximal so as to create a zone of interference 11. Communication with the devices in that zone can be affected by communications with a non-subscribing hub, so as to introduce possible packet transmission collisions and interference. However, because these networks are short-range, the zone of interference 11 is relatively small, and the frequency of collisions and interference is likewise negligible. Proximal operators of such networks can experience impacts, but because of the short-range and the short transmission time of packets, these impacts are minor and usually acceptable.

In contrast and as shown in FIG. 3, three intermediate-range networks are located in similar proximity, each with a hub “H” and subscribing devices “D”. Because of the greater distance of communication provided, most devices “D” are located in zones of interference 11, and many devices may be located in regions 12 where several hubs are located within range. Thus where intermediate-range networks are to be used, most communication between hubs and devices and also inter-device communications should be expected to take place under conditions of interference, especially when located within a city or other populated area. Utility meter reading and other existing installations using the LoRa or LoRaWAN protocols manage this congestion by being the only network in the radio locality on a particular frequency, and by infrequent packet transmission on the order of once per week or month such that collisions between devices aren't likely. Utility meters are configured and installed by the utility provider, who can limit the number of end-devices within a locality to ensure network reliability. Because the provider is the only consumer of the applicable bandwidth resources, it can effectively control interference and manage congestion.

Unavailable on the consumer market today are hubs and end-devices that can operate at intermediate ranges. The short-range “WiFi” 802.11b/g network is now so popular that in most urban areas there is a router within communicative range no matter where a person finds himself; most households using the Internet now have one, purchased from a retailer. If the range of those routers and the devices they service were to be extended to an intermediate range, the result would be a collapse of system functionality from overwhelming interference. Thus, in order to bring intermediate-range devices to the ordinary consumer, further development is needed.

The existing intermediate-range techniques, however, aren't conducive for applications where interactivity is need. For a channel sharing thousands of meters, it isn't necessary to resolve collisions between devices in a matter of milliseconds, because data transmissions can be delayed without significant impacts. In another example, an irrigation controller will ordinarily keep a set of sprinklers on for minutes at a time, and a delay of multiple seconds or even minutes is tolerable. In contrast, a person activating a light switch, for example, will not accept activation of lights with perhaps more than a one-second delay. Where a person enters a code on a keypad to enter a building, he expects a controlled lock to deactivate in real-time. In general, the existing intermediate-range technologies are fault-susceptible and not reliable for such interactivity, particularly where multiple devices share a common communications frequency or channel.

Interactivity issues for battery-powered devices can be even worse. For these devices, it is generally undesirable to keep a receiver continuously powered, and worse to repeatedly being awakened from a sleep mode to process and discriminate packets destined for other devices. The LoRaWAN Class A and B protocols address this by having end-devices turn off their receivers for long periods of time, waking up periodically to interact with a network gateway. Such a device may remain asleep for seconds, minutes or even hours, and thus cannot be made responsive to incoming queries. Furthermore, these protocols are susceptible to collisions from co-transmitting devices, which may require backing off interactions with a hub, and no time of reception can be guaranteed. Thus absent from the field of the invention is a system that can provide adequate and reliable service for groups of sensed and controlled remote devices at intermediate ranges.

BRIEF SUMMARY

Disclosed herein are hub-based wireless networks employing end-devices at intermediate wireless ranges of thousands of meters, utilizing packets that include a preamble and a data payload. End-devices may be such things as keypads, door latches, occupancy monitors, sprinkler controllers and other devices controlled or monitored in a campus or a collection of buildings. A digital spread-spectrum frequency hopping rotation is used, wherein packet transmissions rotate through frequency sequences to spread radio-frequency emissions impact over a set of frequencies. A spectrum-impact-smoothed channel set is fashioned using sequences that each specify a unique preamble frequency relative to the other sequences and channels. The set is traversed as packets are transmitted, thereby distributing the focused radio-frequency emission impact of packets having long preambles over time. Detailed information on various example embodiments of the inventions are provided in the Detailed Description below, and the inventions are defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a network topology utilizing multiple end-devices and an interactive hub.

FIG. 2 depicts potential interference in two proximal short-range wireless networks.

FIG. 3 depicts potential interference in three proximal intermediate-range wireless networks.

FIG. 4 shows an exemplary wireless data packet structure that includes a preamble and a variable payload.

FIG. 5 illustrates an exemplary frequency-sequence table usable in digital spread-spectrum communications between a hub and an end-device.

FIG. 6 depicts typical power states of an end-device through the course of reception of one kind of intermediate-range wireless packet.

FIG. 7 shows an exemplary set of discrete and orthogonal wireless channels for communication between a hub and a set of end-devices.

FIG. 8 shows an exemplary circuit architecture suitable for an ordinary end-device.

FIG. 9 shows an exemplary circuit architecture suitable for a hub having one transmitter and a number of receivers for simultaneous operation on differing channels.

FIG. 10 illustrates the operation of a wireless device on one side of a DSS communication link having a microcontroller and a transceiver.

FIG. 11 depicts a procession of packets including a synchronization directive of successive SIS channel switching.

FIG. 12 depicts a representative accumulated emissions on a frequency spectrum for a transmitter operating using a single DSS channel and preamble-based packets.

FIG. 13 shows traversal of a microcontroller through an exemplary set of states using an spectrum-impact-smoothed channel set.

DETAILED DESCRIPTION

Shown in FIG. 1 is an exemplary intermediate system employing a hub-type topology. A hub 1 is placed within wireless range of end-devices 2a-n, communicating 3 over the airwaves at a distance of up to 10 km or more, depending upon environmental conditions. In many cases, end-devices 2 are electronic devices that accept commands and transmit information to a controlling hub 1. Included in hub 1 and each of end-devices 2a-n is a processor, software for performing the functions of the device, and an RF transceiver. The transceiver may comprise a circuit board comprising a plurality of interconnected planar V-shaped antenna segments. Hub 1 could be an ordinary personal computer with an RF adapter or card installed, or it might simply look like a box with an antenna and a port or interface permitting configuring and monitoring; it is foreseen that a manufacturer would likely supply a hub 1 in a ready-to-use state such that an installer need not open its case or install any software. In one configuration, hub 1 is connectable to a personal computer 4, for example through a USB interface, computer 4 having installed thereon software functional to configure and monitor the hub 1. In another configuration, hub 1 has a network port whereby communications may be had with network 5. These communications may be through any conceivable type or protocol. In one example a hub 1 sends messages through a TCP/IP sockets-based protocol to a proprietary server existing on the network 5. In another example, hub 1 has software that permits it to be seen as an HTTP server from any device on network 5. Thus in some installations, hub 1 may be connected directly to and accessible from the Internet, allowing for access from any Internet-connected device. The antenna of hub 1 will typically be elevated and located in an obstruction-free locality to maximize signal-strength with end-devices 2.

End-devices 2 are preferably manufactured in an unconfigured state, ready for pairing with a hub 1, each device having a unique identity (UID) to discriminate it from others. Such end-devices 2 can be of varying types, providing many kinds of control and sensing functions. In one example, an end-device has an infra-red motion sensor built in, includes programming to record the time of the last motion event, and may also include programming to initiate a notification packet to a hub 1 upon a motion-sensing event. In another example, an end-device includes a keypad whereby a person can enter a code, upon which a message is sent to hub 1 containing a sequence of keypresses. Such an end-device may be paired with another device which activates and deactivates a door latch, by way of messaging from hub 1, and the hub contains programming and configuration to read the keypad end-device and control the latch end-device as correct codes are entered. In a further example, several end-devices 2 are located throughout a building, sensing the temperature at various locations. Another end-device 2 controls a central-air system, providing heating and cooling to the building at the direction of hub 1 without human intervention based upon thermostat data forwarded through hub 1. The kinds of end-devices 2 that can be employed are virtually limitless, so long as they are electronic and provide either a control or a sensing function while staying within the available data throughput limitations.

Intermediate-Range Packets and Transferrence Basics.

Described herein are electronic devices that are functional at intermediate ranges even in populated or congested areas, providing for simple installation by an ordinary home- or business-owner, as will presently be described and shown. These devices can be made reliable enough to use in failure-intolerant situations, such as security systems, even where an RF spectrum is congested. Remote devices can be made to operate on battery power, use low-power transmitters, and in many cases made to operate through the sending of a single bit per packet. Equipment can be made to fit in a hand-held enclosure, e.g. with a small omnidirectional antenna operating in the UHF frequency band. It is sometimes the case that a low-data rate network device will be desired to be placed in a location where power is available, but where neither network cabling nor a WiFi network is available. This kind of application is particularly suitable for intermediate range equipment. One kind of intermediate-range technology is known as “LoRa”, descriptions of which are publicly available from the LoRa Alliance of San Ramon, Calif., which maintains a website at www.lora-alliance.org.

Shown in FIG. 4 is the structure of a simple data packet which may be used in communication between a hub and an end-device, a sub-type of which is used in the LoRa protocol. The structure has three parts, which are a preamble 20, a data payload 22, and an optional address 21. Payload 22 is generic and can contain many kinds of data as desired, depending upon the functions provided by an end-device. Payload 22 will often contain a command or a response, for example a command to open a latch or a response that a power switch is presently in an “on” state. Address 21 discriminates between devices operating on the same communications channel, and may not be needed where a single hub and end-device pair are the sole devices operating on that channel. (A description of what defines a channel appears below.) Preamble 20 is present to provide synchronization for a radio-frequency receiver, at a hub or an end-device, at a programmed frequency such that the receiving device can decode the contents of the packet. A preamble is preferably a fixed, identifiable and unnatural pattern that can be recognized by a simple state machine without starting a general-purpose processor. The packet structure of FIG. 4 can be transmit using many modulation techniques; LoRa devices use frequency shift keying for interference immunity, although other modulations can be used in accordance with the dictates of a particular operating environment.

Packets can be transmit over a single carrier frequency, if desired, but because of benefits including resistance to noise and reduced impacts on particular parts of a frequency spectrum, spread-spectrum modulation has become popular. In this modulation technique, a sequence of frequencies is provided at a transmitter and a receiver; although in traditional encrypting systems the sequence might be generated by a pseudo-random generator with a secret seed and function parameters (which still can be used), for noise resistance and spreading of Tx power all that is needed is a sequence of frequencies uniformly spread over a given available set. This can be accomplished by the inclusion of a table as shown in FIG. 5, containing a sequence of n frequencies. In the example, each frequency F_x is indexed by a sequence number I_n, such that the current operational frequency can be determined as a function of time from a point of synchronization, for example the end 23 of the preamble of a packet as in FIG. 4. The arrangement of frequencies in a sequence may be incremental, random, or in any order desired, keeping in mind that use of each frequency an equal number of times will result in the desired uniformity.

The transmission of a packet using this modulation technique is as shown in FIG. 6, beginning with the preamble at a known initial frequency F₀. The preamble is preferably not just a square wave, but a pattern whereby synchronization point 23 can be positively determined. The transmitter then sequences through the frequencies at a known period, mirrored by the receiver. For noise and interference immunity the sequence period is preferably much shorter than the time needed for each bit or symbol, but longer periods can be used to achieve a spreading of power across a spectrum. The sequence period should preferably be much shorter than the time of preamble transmission, such that preambles are easy to distinguish.

The power consumption of a transmitter is necessarily high during packet transmission, most of the power likely being consumed by the Tx output stage circuitry. A receiver, on the other hand, can implement a power-conserving procedure. Referring again to FIG. 6, the processor of a receiving device maintains itself in a state of sleep 25 while processing and receiving activities aren't underway; this can be particularly important for certain kinds of devices, especially for end-devices reliant upon battery-power, such as those with solar cells. A receiving device has built thereinto its receiving circuit an automated preamble recognizer; when recognition occurs a signal is sent to a processor to awaken and enter an active state of packet decoding 26. In the example of FIG. 6 an address is used, and the receiving processor performs functions needed to determine if the address in the packet is for its device. If an address is decoded and the packet is determined to be destined for another device, the processor can reset and go back to a sleeping state 25. For maximal power savings, therefore, an address is preferred to be toward the front of a packet, where it will be transited across a channel first before a data body. Where an address is matched, or where an address isn't used, a processor enters states of receiving and processing incoming data 27 and post-receipt processing 28 as needed. So in order to keep the processor of a particular device in a non-active state, it is important to positively discriminate the receipt of preambles of packets directed to the device from the preambles of other devices.

Multi-Channel Intermediate-Range Implementations.

Existing intermediate-range networks use a common initial DSS frequency and/or channel for communications with devices in that network. This method has the advantage of making setup extremely simple. By this method, other networks may use other initial frequencies or channels, thereby discriminating between members of their respective networks. As such networks change to include interactive devices or grow to large numbers of member devices, the possibility of congestion, collisions and interference becomes a greater concern.

Now turning to FIG. 8, a basic circuit is shown typical of many present intermediate-range network devices, which can support either single- or multiple-channel operation. The main parts of this circuit are a microcontroller 30 and an RF transceiver 32, which is connected to an antenna 34 located in a position to provide clear communications to other devices. A transceiver 32 may be essentially some analog radio-frequency circuits combined with a logic state machine that permits automatic operation for all or part of a packet transmission or reception. The use of transceiver 32 may leave the microcontroller 30 with additional processing capacity for such things as reading sensors, managing control circuits, etc., which may happen at the same time that packets are transiting a communications channel. Communication between the microcontroller and the transceiver is by way of data lines 39 and interrupt lines 40, by which microcontroller 30 manages the functions of transceiver 32 and transfers packet information received and to be sent. Transceiver has a packet buffer 45 sufficient to store all or part of a single packet, read- and write-accessible through data lines 39. Data lines 39 can be varied according to need or capabilities of a transceiver used, while interrupt lines 40 signal to the microcontroller events such as the start or completion of reception of an incoming packet. Were transceiver 32 to be a Semtech SX127x (introduced below), for example, data would be transferred by way of a single-bit wide serial bus using address locations to control registers and access a packet buffer, and data lines 39 would include single lines for in, out, clock and sync. In that example, a packet completion interrupt would be generated by a transition on the DIO0 line. When transceiver 32 is configured for operation on a channel orthogonal to those used by other end-devices, such interrupts would not occur when those end-devices communicate and microcontroller 30 would be left free to sleep or engage in other processing activity.

Microcontroller 30 also contains a packet buffer 44, which is typically larger than the transceiver buffer 45. As packets are to be transmitted, the microcontroller transfers them to the transceiver by way of data lines 39, typically one at a time. Packets received are correspondingly transferred from buffer 45 over the data lines and stored for processing in buffer 44. Apart from this packet data, setup commands are also sent by microcontroller 30 to program the transceiver for proper operation on a channel, once at initialization for single-channel operation and subsequently with or between packets where more than one channel is used. Where microcontroller 30 has been programmed for multi-channel operation, each packet within buffer 44 may carry with it a channel on which it is to be sent, or parameters thereof.

In an implementation using the Semtech SX127x and digital spread-spectrum, microcontroller 43 also contains a frequency table 43, as described above for FIG. 5. For that implementation, the transceiver 32 has storage only for two frequency settings, which are the one presently in use and the one to be used when it is time for a hop to a new frequency. The transceiver generates interrupts to the microcontroller indicating it is ready to receive the new frequency setting, which is subsequently sent over data lines 39 before the frequency hop is to occur. An alternate configuration would put frequency table 43 entirely on the transceiver 32, but for this example a simplified transceiver is used that does not.

Where a transceiver 32 and microcontroller 30 pair is incorporated into an end-device, at least one of a sensor 36 or a controller 38 will be included. Sensor 36 could be virtually any sensor, examples of which are a temperature probe, a keypad, a lighting sensor, an entryway closure detector, a motion detector, and a camera. Controller 38 could control a latch, a power switch, a thermostat, a motor speed controller, and many other things. Sensor 36 and controller 38 are connected to microcontroller 30 through data lines 41 and 42, which lines may be of any needed configuration, analog or digital. Where a transceiver 32 and microcontroller 30 pair is incorporated into a hub, sensor 36 and controller 38 may be omitted. Instead, a connection to a host processor or network 48 would be included, permitting configuration of and interactions with end-devices at intermediate-range.

While functioning as an end-device, one microcontroller 30 paired with one transceiver 32 are sufficient to operate in an ordinary way. Transceiver 32 is capable of being configured for a desired channel and transmitting or receiving packets to and from a hub, though not at the same time. End-devices do not typically have a need to do both concurrently, so this is usually not an issue. However there are advantages to incorporating multiple transceivers in a hub, as will be presently explained.

FIG. 9 illustrates one configuration that may be used in a hub, providing multiple transceiver functionality. Here a microcontroller 30 is connected to n transceivers 34a through 34n by way of an interrupt gate 50 and data bus 51. Included within data bus 51 is sufficient multiplexing circuits to allow the microcontroller 30 to individually address each transceiver. In the example where the Semtech SX127x transceivers are used, this may be done by dropping the NSS pin of the individual transceiver to be attended to. Interrupt gate 50 combines the interrupt signals of each of the transceivers such that any interrupt in the group interrupts the microcontroller, and code therein can identify the particular transceiver flagging the interrupt and take appropriate action. In the drawing gate 50 is an OR logic gate, which suffices when all interrupt lines are low in a normal (non-interrupt) state; gate 50 could be AND logic gate if the reverse were true (lines normally high with low signal indicating an interrupt), or gate 50 could be a combination of logic circuits if needed. Now in practice it may be there are a sufficient number of interrupt inputs and general I/O pins on microcontroller 30 such that gate 50 and bus 51 aren't needed, particularly where the number of transceivers n is kept small, allowing for the microcontroller to communicate using parallel lines duplicating the setup and methods of FIG. 8.

The exemplary hub of FIG. 9 has the capability of transmitting and receiving wirelessly with end-devices at the same time, through antennas 34a and 34b. Antenna 34b is connected as an input to each of transceivers 32b through 32n, allowing each transceiver to receive on a different channel as programmed from the microcontroller 30. Depending upon the type of transceiver used, each transceiver may be isolated through filters and amplifiers (not shown) such that the proper impedance at the operational frequency range is preserved. Note that such a tying of transceivers to a common antenna makes them ineffective for concurrent operations in a transmitting mode; therefore microcontroller 30 would be configured to keep them in receiving-mode only. In contrast antenna 34a and transceiver 32a are configured to transmit and receive, having no sharing of antenna resources. Consideration should be given to shielding and to the distance between an antenna that may be used for transmitting and others that may be used for reception, such that potential interference is avoided. The transceiver may comprise a circuit board comprising an antenna comprising a plurality of interconnected planar V-shaped antenna segments as taught in co-pending U.S. patent application Ser. No. 15/458,347, the entire contents of which are incorporated herein by this reference.

The example shown in FIG. 9 has the capability of transmitting and receiving at the same time, with n−1 receivers monitoring one channel each. Transceiver 32a can be transmitting while all of 32b-n are ready to receive packets as they may transit n−1 channels. Microcontroller 30 may use the transceiver capable of free transmit operation 32a to perform interactive communication with an end-device without channel reprogramming, alternating between sending and receiving over the same channel. Alternatively, when using interactive communication with a particular end-device, microcontroller 30 may command transceiver 32a to switch to different channels as needed for transmissions to other end-devices, allowing one of transceivers 32b-n to receive the next packet from the particular end-device. If this is done, it is preferred that any transceivers configured to receive on the same channel be turned off, so as to avoid the discarding of packets produced at the hub. Assuming interactions with an end-device are symmetric in length, in theory the setup shown in FIG. 9 will support up to two concurrent interactive sessions with two end-devices while at the same time monitoring n−2 other lone-channel end-devices for alerting packets sent spontaneously, or more than that number of end-devices where such channels are shared (using the asynchronous mode described below, for example.)

In practice, the constraints on the number of transceivers that can be used will depend upon several factors. One of these is the speed of data bus 51 against the efficiency of commanding transceiver setup, and sending and receiving packet data. As most of the transceivers of the setup of FIG. 9 are used to receive, this limitation would be experienced in two main ways. First, it is possible to flood the system with incoming spontaneous packets such that they cannot be retrieved with sufficient speed across bus 51. The second way comes into play when single receivers 32 are each used to monitor multiple channels, for example when the number of monitored channels exceeds n−1. The reprogramming of a transceiver 32 across the bus 51 requires some time, and if that time exceeds the packet preamble length, packets will fail to be received. Where more than two channels are monitored by a single transceiver 32, the dwell time on a channel (to detect whether a packet transmission is in progress by an end-device) may further exacerbate this problem.

Another limitation of the setup of FIG. 9 relates to the use of a single transmitter. For example, interactive communication can be had with not more than two end-devices where that communication is symmetric. Thus if an event occurs that requires a simultaneous response to multiple end-devices, some of those responses may be delayed beyond a timeout period. This problem can be mitigated through the addition of more transceiver/antenna pairs, if those antennas can be placed at a sufficient distance from the receiving ones and if regulations allow. The transceiver may comprise a circuit board comprising an antenna comprising a plurality of interconnected planar V-shaped antenna segments as taught in co-pending U.S. patent application Ser. No. 15/458,347, the entire contents of which are incorporated herein by this reference. Note that although end-devices can be constructed with multiple transceivers, as in FIG. 9, it is expected that one transceiver will be sufficient for all but the most exceptional circumstances.

Wireless Channels, Orthogonality and Communications Principles.

A wireless frequency spectrum can be segmented into definite channels that reduce interference and avoid unnecessary receiver power-up events on non-destination devices. Such channels are preferably “orthogonal” to each other as well, meaning that communication on one channel is very unlikely or practically impossible to interfere with communication on another. In one of the simplest channel designation schemes, each channel is assigned a unique and available center frequency per channel, for example as was done on the now-obsolete analog television spectrum. A one-to-one relationship is made between transmitters and frequencies in a radio locality, and all devices are to use only their assigned spectrum and nothing outside. For example, the 902-928 MHz ISM band could be divided into 52 500 kHz-wide channels, or 208 125 kHz-wide ones. Given that an intermediate network supporting ordinary consumers might have a range of many kilometers and thousands of end-devices, that is considered an insufficient number to avoid interference. Therefore further methods of discrimination are preferably used.

Introduced now are certain transceivers made for the LoRa protocol, commercially available from Semtech Corporation, which are identified as the SX127x product line. Note that there are transceivers available from other manufacturers that are equally suitable; these Semtech ones are used in this description merely out of convenience as a basis for discussion. The SX127x products are designed to be coupled to a microcontroller handling communication channel configuration and packet management, and have settings for a carrier frequency, signal bandwidth and the number of “chips” per symbol (6 settings), a chip being the smallest datum used in communication. Each combination of those represents substantially a unique channel orthogonal to others, potentially permitting collision-free communication where there is no more than one transmitting device per channel. Using such combinations, two channels may share a common carrier frequency or DSS carrier sequence, while still maintaining orthogonality. Other settings can be used to make additional channels having “partially-orthogonality” including an address, a bit rate, a CRC rate, an encoding type (Manchester/whitening/none), and others according to the manufacturer specifications; note however that the use of partially-orthogonal channels can result in processor-awakening events for packets destined for unintended end-devices, although they can be greatly reduced.

Upon identification of a useful set of channel combinations, a table can be constructed as shown in FIG. 7, each channel having a unique combination of settings useful for communication. In this example, each channel is assigned a spread-spectrum frequency sequence (FS), a spreading factor (SF), and a bit rate (BR) of communication. In one configuration, available frequency sequences are spread evenly over channel assignments, such that the preamble for each channel is sparsely or uniquely used—that is a device transmitting a packet on an assigned channel would use the first frequency in the sequence while transmitting the preamble, followed by the use of other frequencies in sequence. Other channel combinations can be varied in accordance with needs present, for example a frequency sequence could be replaced with an operating frequency where spread-spectrum communication was not used.

Upon determining a set of channel combinations, assignments can be made for individual devices. Again some devices are tolerant of long latencies, and no special treatment of these is required. Other devices serve better being on a channel that is free or substantially free of conflicts. The assignment of a channel to a hub and an end-device requires a setting at both, and this could be made by a manufacturer or its representative at the time of installation.

Frequency Sequence Processions and Spectrum Impact Smoothed Channel Sets.

Where packets carrying a preamble such as that shown in FIG. 6 are used, the impact to the frequency F₀ in the usable spectrum is larger than the impact to other frequencies F_a through F_n generally. This effect is caused in large part by the long time used in transmitting the preamble, during which time the transmitter must remain on the same frequency F₀ for synchronization as compared to the other successive frequencies used. The longer the preamble with respect to the packet, the more exaggerated is this effect. Additionally, the frequencies at the end of the sequence toward F_n are used less frequently, due to the end of packet usually occurring in the middle of the frequency sequence, which may be exaggerated by short packets. As seen over time, if a frequency sequence is used continuously the impact on the spectrum of usable frequencies will be as depicted in FIG. 12, with accumulated emissions over time E_T focused on the preamble frequency F₀ and an uneven impact ramping down through the frequency sequence.

This focused impact can be avoided through rotation of channels, each having a different frequency sequence and a unique F₀ used in a preamble relative to the other channels used in the rotation, hereinafter referred to as a spectrum-impact-smoothed (SIS) channel set. So looking back to FIG. 7, an SIS set maintaining the same bit rate and spreading factor could be fashioned from channels 0, 2, 4 and so forth, and another sequence could be ordered 1, 3, 5, etc., provided that the channels in each sequence included an F₀ unique to the others in that sequence. Within the set of sequences, where each frequency used occupies each sequential position no more than once through the channel set, the smoothing effect can be increased, although that is not necessary. Using the representation of FIG. 5, if there are n=72 frequencies usable in a DSS sequence, each would occupy the I₀/F_a position exactly once through all sequences to make an SIS channel set of 72 channels. Preferably, each frequency would also occupy each I₁/F_b through I₇₁/F_n position exactly once as well to maximize the evening effect in the spectrum.

Frequency sequences can be generated and stored beforehand, or generated on the fly as needed. In a simple example, 72 adjacent ordered frequencies are available for use, and a set of SIS channels are generated by choosing a unique starting preamble frequency F₀ having the same position in the order as the channel number, each frequency in the sequence rising though the order and wrapping around as needed. In another example, an order is generated randomly, assigning one channel to each preamble frequency. In yet another example, a simple calculation or a pseudo-random number generator uses the channel number and the number in sequence to arrive at a frequency as needed. In the example shown in FIG. 5, the frequency used for the preamble is left unused for the remainder of a packet transmission, assisting in the equalization of frequency impacts where short packets are the norm. That is not required; a preamble frequency F₀ can be repeated, particularly where traversal through a sequence is also repeated where a packet is long.

As described above, the synchronization of frequency hopping through a series of frequencies can be done through detection of the end of a preamble. Two sides of a communication link will also need to be synchronized with respect to a channel, as traversal proceeds through an SIS set. That synchronization can be to any event shared between the sides, such as the traversal of a packet of a particular type or carrying a particular identity. In one example, a timeout period is used for synchronization: where a packet hasn't traversed the link for a specified period of time, both sides synchronize on the initial channel of an SIS set. This may also provide a fail-safe mechanism for dropped packets, allowing resynchronization in case of error.

In one implementation, two sides of a communications link utilizing an SIS set switches channel following every packet traversing the link, without further direction or instruction. The devices on both sides of the link follow a set of rules, including an order of traversal through the SIS channel set used. In one variation, the channels are used in an incremental order using a simple index variable, proceeding through channel 0, channel 1, channel 2 and so forth with each packet, wrapping around back to zero when all channels have been used. In another variation, the order of channels used follows a pattern stored in memory in a table or other structure. In yet another variation, a next channel is calculated using a pseudo-random formula using an incrementing index or the index of the channel currently being used, retaining other communication parameters such as bit rate, spreading factor, etc. In yet another variation, a microcontroller performs a calculation to evaluate the emissions impact on frequencies used since the beginning of traversal through the SIS channel set, and the next channel is selected to have a preamble frequency impacted less than the others since traversal began, thus maximizing the evening effect. A next SIS channel may generally be determined using a computation deterministic from information residing in the memory of both devices. In yet another variation, a next SIS channel is determined using a computation deterministic from information in a previously exchanged packet. The determination and of a next channel can have wide variation, as well as the timing of procession through a channel set, and what is important is that both devices in a communications link use cooperative rules and iterate through an SIS channel set in the same order.

FIG. 10 illustrates in further detail the operation of a device on one side of a communications link using DSS communication, the device including a transceiver 82 of a type including the Semtech 127x transceiver in conjunction with a microcontroller 81. Transceiver 82 includes a register FC for the current frequency being used in transmission, a register FN for the next frequency to be used, and a packet buffer PB containing the contents of a packet being transmitted, as well as other programmable registers used in setup and operation. To initiate a packet exchange, the microcontroller 81 identifies a frequency sequence of a channel 83 (which may be that of an SIS channel), and transfers the first frequency value f₀ and the next frequency value f_a to those registers on the transceiver as shown. If the exchange is a transmission to the device on the other side of the link, all or part of the contents of a packet will also be transferred to the packet buffer on the transceiver 82. When the registers on the transceiver 82 are loaded and communications setup has been completed, the transceiver is commanded to initiate communication. The transceiver may comprise a circuit board comprising an antenna comprising a plurality of interconnected planar V-shaped antenna segments as taught in co-pending U.S. patent application Ser. No. 15/458,347, the entire contents of which are incorporated herein by this reference.

For both transmission and reception, as DSS communication proceeds transceiver 82 frequency hops, moving the value of the next frequency FN to the current frequency FC. Before the time of the succeeding hop, microcontroller 81 is interrupted, and a succeeding frequency value is transferred to FN from the identified frequency sequence 83. Eventually the packet exchange will complete, and microcontroller 81 will be interrupted to do whatever post-processing is needed, including a reading of the transceiver's packet buffer PB if a packet was received.

As introduced above, synchronization of a traversal through a set of SIS channels may simply occur for each packet, channel switches occurring therebetween. Another method of synchronization is depicted in FIG. 11, wherein a “left” device synchronizes SIS channel switching with a “right” device over a wireless link through information contained in transmitted packets. Proceeding down the page, both devices are initially synchronized on channel 00, the right device in a listening mode prepared to receive a packet. The left device transmits a packet 101 on channel 0. Packet 101 includes a preamble, the address of the right device “RR”, and a payload portion. Contained within that payload is a directive 101a to change to channel 01. Following the exchange of packet 101, the right device transmits an acknowledgment 102 to the left device on channel 00, which serves as confirmation that the right device will listen for future packets on the new channel as directed. Following the exchange of packet 102, both the left and the right devices are synchronized on channel 01.

The left device may send another packet 103 containing a directive 103a to change to channel 2. This packet is not received by the right device, so no acknowledgment is returned and a timeout 104 occurs. In such an event, the left device may resend 105 the packet containing the same directive 103a, until that directive is received and acknowledged 106 by the right device. Should an acknowledgment packet not be received by the left device, both devices may timeout and revert back to a default channel. As continuing to transmit the same packet would increase the impact on the preamble frequency of the current channel in use, it is preferable to limit the number of retries to a predetermined number.

It may be desirable to use the current SIS channel for transmissions from both devices while communicating, so as to equalize the spectrum impacts of transmissions from both devices at the same time, although that is not necessary. One device, such as the right device in the example of FIG. 11, may utilize a separate channel for acknowledgments or packets generally, or may even use an indepedent SIS channel selection for transmissions to another device on the other side of a link.

Depicted in FIG. 13 are the states of a state machine suitable for implementation in a microcontroller utilizing an SIS channel set, in a configuration shown in FIG. 10. After initialization or during normal operation, the microcontroller may determine that it is time 120 to send or receive a packet to or from the device at the other side of the communications link. If more than one transceiver is available to use, then one of them may be selected at this point. In this implementation, the next step is to determine a value next_channel, which is to be the succeeding SIS channel used. Where the device receives a channel directive by way of packets, this determination may be omitted.

The transceiver is then programmed 124 with a current frequency FC and a next frequency FN for DSS frequency hopping, to be done as in FIG. 6, coming from the current channel frequency sequence. This programming may be done through lookup in a table, or by computation, as desired. An index into the frequency sequence is set 126 to FSI=2, pointing to the third frequency in the sequence.

The machine then must take some extra actions if the device is sending a packet 128. These actions are to build a packet in a buffer 130, in accordance with whatever protocols are used by the present and remote devices. If the present device is determining the next channel for the remote device, part of this built packet may contain a directive to move to the next_channel determined earlier. The built packet is then copied to the transceiver 132, the state is set to transmitting 134, and a command is sent to the transceiver to transmit the packet in its buffer 138. If the device is merely receiving packets 128, then the state can be set to that 136 and the transceiver commanded to receive 140, having been properly configured with all necessary communications parameters.

Following the commanding of the transceiver, a sleeping state 142 may be entered. Now it is to be understood that this state could shutdown the microcontroller entirely until something further happens, or this state could indicate that the processor is free to manage other tasks. For example, a device implementing a sensing function that reports only when prompted may sleep for long periods of time, awakening only to manage long timeouts and other maintenance functions. In another example, a device managing multiple transceivers such as a hub may leave the state in sleep for the present transceiver, turning to manage other transceivers or functions as needed. Regardless, for discussion purposes the state machine may remain in a state of sleep until certain events happen.

While in sleep mode, interrupts 150 will be generated by the transceiver. When they are, there are several state paths that can be taken. If the next frequency register FN has been copied to the current frequency register FC, it will be dry 152 and need to be reloaded. If that has occurred, the next frequency in the sequence will be set 154, and the index incremented 156. If the index exceeds the number of channels in an SIS sequence, it may be set to 0 (the preamble frequency) or 1, avoiding re-use of the preamble frequency. If the packet has been fully exchanged 158, the main thread may be awakened 160 to exit the state of sleep. If the interrupt occurred for some other cause, such as the expiration of a timer or an alarm event, other processing 162 may occur in response. Interrupt processing will end 164, and the microcontroller may return to a state of sleep or may proceed in an awakened state.

When awakened, the current channel will be rotated 144 with the next channel determined earlier, and any post-processing needed may be done 146. That post-processing may include retrieving and decoding a packet if one was received by the transceiver, and may further include the setting of a current_channel, when directed from the device on the other side of a link.

To avoid timeouts that cause a reversion back to a default channel, periodic packets may be sent at an interval less than the timeout period, which packets may be simple “ping” packets.

The teachings regarding SIS channel sets can be applied to two devices in a simple point-to-point fashion, or to multiple devices in varying interactions such as hubs and end-devices. Where a hub is used, a frequency sequence index may be kept for multiple devices, such that spectrum impacts can be smoothed with respect to individual of those devices.

Now although certain systems, products, components, functions and methods have been described above in detail for specific applications, one of ordinary skill in the art will recognize that these functions and methods are adaptable to other systems and products. Likewise, although the described functions have been described through the use of block and state diagrams, flowcharts, and software and hardware descriptions, one of ordinary skill in the art will recognize that most of the functions described herein may be implemented in software or hardware. State machines described herein may likewise be implemented completely in logic, as software executable on a general-purpose or embedded processor, or as a mixture of both. Some of the descriptions herein refer to specific protocols and modulation types, which are only exemplary; other protocols and types may be substituted as desired in accordance with the inventive concepts. More specifically, it is to be understood that although the accompanying description makes reference to the LoRa and LoRaWAN protocols and designs, the inventions described herein may be used in other kinds of intermediate-range networks, RF bands and using other equipment. The exact configurations described herein need not be adhered to, but rather the diagrams and architectures described herein may be varied according to the skill of one of ordinary skill in the art. Therefore, the inventions disclosed herein are to be fully embraced within the scope as defined in the claims. It is furthermore understood that the summary description and the abstract are provided merely for indexing and searching purposes, and do not limit the inventions presented herein in any way.

Claims

1. A pair of wireless communications devices operational at intermediate ranges, said pair of wireless communications devices utilizing a set of discrete radio frequencies upon which are organized a set of spectrum-impact-smoothed (sis) channels each having a distinct digital spread spectrum frequency sequence, each sis channel specifying a unique frequency to be used in the transmission of a packet preamble relative to all of the other sis channels within the set, each of said pair of wireless communications devices comprising:

a transceiver functional for wireless communication using the frequency sequence of the spectrum-impact-smoothed channels; and

an electronic circuit implementing a state machine immutable to power-transient events;

wherein said state machine of each device is configured to sequence through a set of states to

2. The pair of devices as recited in claim 1, wherein said state machine of each device is configured to sequence through a set of states to implement a function of transferring to said transceiver of the particular device a next frequency in the digital spread spectrum frequency sequence in use during a packet exchange.

3. The pair of devices as recited in claim 1, wherein one of said pair of wireless communications devices is configured to send an identification of a determined next sis channel to the other of said pair of wireless communications devices in the course of transmitting a packet.

4. The pair of devices recited in claim 1, wherein said state machine of each device is configured to sequence through a set of states to implement a function of calculating an emissions impact on frequencies in the sis channels used in the course of traversing the sis sequence to the exchange of a previous packet, and

said determining a next sis channel is made using frequency impact calculations, and in the course of said determining a next sis channel is selected having a preamble frequency with a low calculated emissions impact so far in a traversal of the sis channel sequence.

5. The pair of devices recited in claim 1, wherein said determining a next sis channel is made using a pseudorandom function.

6. The pair of devices recited in claim 1, wherein said determining a next sis channel is made using a set of frequency tables stored in memory.

7. The pair of devices recited in claim 1, wherein each device includes a memory, and wherein said determining a next sis channel is made using a computation deterministic from information residing in the memory of both devices.

8. The device recited in claim 1, wherein the transceiver comprises a circuit board comprising a plurality of interconnected planar V-shaped antenna segments.

9. A wireless communications device operational at intermediate ranges, said device utilizing a set of discrete radio frequencies upon which are organized a set of spectrum-impact-smoothed (sis) channels each having a distinct digital spread spectrum frequency sequence, each sis channel specifying a unique frequency to be used in a transmission of a packet preamble relative to all the other frequency sequences of the sis channels within the set, said device comprising:

a transceiver functional for wireless communication using the frequency sequence of the spectrum-impact-smoothed channels with another wireless device; and

an electronic circuit implementing a state machine immutable to power-transient events;

wherein said state machine of said device is configured to sequence through a set of states to implement functions of:

(d) configuring said transceiver to transmit or receive a packet on a channel having distinct communication parameters,

(e) synchronizing with another wireless device on a first communications channel in the set of sis channels, said synchronizing initiating a sequence of sis channels beginning with the first communications channel,

(f) exchanging a packet with another wireless device synchronized on a first communications channel in a sequence of sis channels,

(g) repeatedly determining from a current sis channel a next sis channel to be used in exchanging a packet with another synchronized device, said determining selecting a channel not yet used in the sequence of sis channels beginning with a first communications channel,

(h) repeatedly exchanging a packet with another synchronized device using a determined next sis channel.

10. The device recited in claim 9, wherein said state machine of said device is configured to sequence through a set of states to implement a function of transferring to said transceiver a next frequency in the digital spread spectrum frequency sequence in use during a packet exchange.

11. The device recited in claim 9, wherein said device is configured to send an identification of a determined next sis channel to said device in the course of transmitting a packet.

12. The device recited in claim 9, wherein:

said state machine is configured to sequence through a set of states to implement a function of calculating an emissions impact on frequencies in the sis channels used in the course of traversing the sis sequence to the exchange of a previous packet, and

said determining a next sis channel is made using frequency impact calculations, and in the course of said determining a next sis channel is selected having a preamble frequency with a low calculated emissions impact so far in a traversal of the sis channel sequence.

13. The device recited in claim 9, wherein said determining a next sis channel is made using a pseudorandom function.

14. The device recited in claim 9, wherein said determining a next sis channel is made using a set of frequency tables stored in memory.

15. The device recited in claim 9, wherein said determining a next sis channel is made using a computation deterministic from information in a previously exchanged packet.

16. A wireless communications device operational at intermediate ranges, said device utilizing a set of discrete radio frequencies upon which are organized a set of spectrum-impact-smoothed (sis) channels each having a distinct digital spread spectrum frequency sequence, each sis channel specifying a unique frequency to be used in a transmission of a packet preamble relative to all of the other frequency sequences of the sis channels within the set, said device comprising:

a transceiver functional for wireless communication using the frequency sequence of the spectrum-impact-smoothed channels with another wireless device; and

an electronic circuit implementing a state machine immutable to power-transient events;

wherein said state machine of said device is configured to sequence through a set of states to

17. The wireless device recited in claim 16, wherein the state machine of said device is configured to detect desynchronization after a timeout period without a successful packet exchange with another previously synchronized wireless device.

18. The device recited in claim 16, wherein said state machine of said device is configured to sequence through a set of states to implement a function of transferring to said transceiver a next frequency in the digital spread spectrum frequency sequence in use during a packet exchange.

19. The device recited in claim 16, wherein said device is configured to end an identification of a determined next sis channel to another synchronized wireless device in the course of transmitting a packet.

20. The device recited in claim 16, wherein said determining a next sis channel is made using a computation deterministic from information in a previously exchanged packet.